This is the easiest way to cut up a pineapple for eating out of hand:
Get a large knife.
Twist the top off the pineapple.
Cut the bottom off.
Stand the pineapple up and slice down through the core cutting the pineapple into halves.
Cut each half in half through the core.
Now stand each quarter up and slice the core away.
Lay each quarter back down, fruit side up.
Slice into wedges.
If you don't want the skin on the pieces do this: Once you've quartered it, lay each piece down fruit side up. Slide the knife along between the skin and the flesh. Discard the skin and cut up the pineapple however you choose.
While delicious, fresh pineapple juice contains enzymes which can be hard on your hands if you handle very much of it. If you are going to be cutting up pineapples a lot, you might want to use a peeler.
There are a couple of different kinds of pineapple peelers. Some remove the skin and some remove the eyes that are left once the pineapple is peeled.
If you want the core removed and the shell left intact, you need a pineapple corer. These amazing devices will core and spiral slice the pineapple for you. They leave you with a shell you can serve a drink in. Great for parties.